Method for hard-surfacing metal edges



United States Patent Ofi 3,097,959 Patented July 16, 1963 3,097,959 METHOD FOR HARD-SURFACING METAL EDGES Neil J. Zachman, Wiliowdale, Ontario, Canada, assigner to Union Carbide Canada Limited, Toronto, Ontario, Canada Filed Nov. 24, 1961, Ser. No. 154,612 2 Claims. (Cl. 117-22) The present invention relates to an improved method for hard-surfacing the edges of metal articles such as knives, chisels, surgical instruments, chain saw guidebars and the like. More particularly, the present invention relates to an improved method for simultaneously hard-surfacing the edges of a plurality of similarly shaped metal articles of the class described.

At present, spray hard-surfacing is a widely employed technique for rendering the edges of metal articles abrasion-resistant. T-he technique of spray hard-surfacing as it is generally practiced comprises preparing a metal work piece by cleaning and roughening the surface, for example by blasting -With aluminum oxide; subsequently directing a forced ow of metallic powder at high temperature at the prepared surface to form a deposit thereon; and ultimately fusing the deposited metallic material by suitable means suclr as an ioxyacetylene torch or induction heating equipment. When applying a deposit of nickel-base alloy or tungsten carbide, the stream of powders is usually pre-heated to about 1200 F. while a pre-heat temperature of about 1500" F. is preferred when depositing cobalt-base alloy powders.

As a result of the fusing operation, the deposited metallic powder shrinks about l5 percent in volume and becomes strongly bonded to the edge of the work piece and provides a hard surface which is highly resistant to heat, abrasion, oxidation, corrosion and thermal shock.

In View of the economic and other advantages which are characteristic of the `aforementioned spray hard-surfacing technique, efforts have been made by the art to provide a method for efficiently and simultaneously hardsurfacing the edges of a plurality of similarly shaped metal articles.

A hard-surfacing method which is typical of the prior art efforts in respect of this problem comprises closely arranging the metal pieces to lbe treated in a stack with recessed spacersbeing arranged between the metal pieces; depositing hard-surfacing metallic powder on the edges of the stacked metal pieces, and heat treating the deposited hard-surfacing metallic material to cause fusion thereof as a result of which the hard-surfacing metallic material becomes strongly bonded to the edges of the etal pieces and experiences a reduction in volume.

After the heat-treating step, the stacked metal pieces are separated and the hard-surfaced edges are machined to the desired dimensions.

A difliculty encountered in the above-described hardsurfacing operation is that after the heat-treating step the hard-surfacing substance forms a complete or partial bridge of fused material between the stacked metal pieces. Under these circumstances it is necessary to rst detach the hard-surfaced metal pieces before final grinding and preparation for their ultimate use. Consequently a timeconsuming and economically detrimental after-treatment is required which detracts from an otherwise highly advantageous and relatively simple process.

It is therefore an object of the present invention to provide an improved method for simultaneously hardsurfacing a plurality of metal articles whereby adhesion between the individual hard-surfaced articles is avoided.

Other objects Will be apparent from the following description and claims taken in conjunction with the drawing in which:

FIGURE l shows a stack of metal pieces arranged in accordance with the present invention onto which metallic hard-surfacing powder has been deposited FIGURE 2 shows the arrangment of FIGURE 1 after fusion of the deposited material and FIGURE 3 shows a stack of metal pieces which have been hard-surfaced without the benefit of the present invention.

The improvement in the aforementioned process for simultaneously hard-surfacing metal articles which is provided by the present invention is the utilization of spacers between the stacked metal articles which spacers extend beyond the edges to be hard-surfaced and which are adhesion-resistant to the hard-surfacing material.

In the present invention, the spacers are extended beyond the metal edges to the extent such that after the heat-treatment 'of the applied hard-surfacing material and the resultant reduction in volume thereof due to fusion, all `of the hard-surfacing material bonded to the metal pieces is confined between the spacers and the undesirable bridging effect is thereby eliminated.

In a specific embodiment of the present improved process, by wedge-shaping Ior tapering the extending portions of the spacers, the necessary amount of spacer extension is minimized and the application of the hard-surfacing material is facilitated.

The present invention will be more clearly understood with reference to the drawing which shows in FIGURE 1 a stack of closely spaced metal pieces 1 which can for example be plain carbon steel guide-bars which are required to be hard-surfaced for use in chain saw apparatus. The metal pieces 1 are separated by spacers 3 which extend beyond the edges of the pieces which are to be hard-surfaced. Clamps 5 are provided to secure the stacked metal pieces and spacers.

yIn order to achieve economy of operation, the separation between the metal pieces is usually quite small, i.e. less than about 1A inch. The spacers are preferably formed of asbestos although copper and other materials, such as surface-oxidized metals and organic compositions which can withstand the temperatures involved, are also suitable. A particular alloy which is suitable as the spacer material has a composition of 0.5 to 2.5 percent cobalt, 20.5 to 23 percent chromium, 8 to 10 percent molybdenum, 0.2 to 1 percent tungsten, 17 to 20 percent iron, 0.05 to 0.2. percent carbon, up to 1 percent silicon, `up to l percent manganese, the balance being substantially all nickel.

After the metal pieces and spacers are arranged as illustrated, a forced stream of hard-surfacing metallic power, suitably preheated, is sprayed yon the edges of the metal pieces to form a ldeposit of hard-surfacing material indicated as 7 in FIGURE 1. The spraying and preheating of the hard-surfacing material can be accomplished by means of iany :of the well-known spray-gun devices manufactured and sold for this purpose.

After the metallic deposit 7 has been formed, it is heated and fused by an -oxyacetylene torch or other suitable means whereby the hard-surfacing material is strongly bonded :to the metal pieces and shrinks in volume about 15 percent as indicated as 9 in FIGURE 2. Due to the reduction of volume and the vpresence of `extending spacers 3, the fused metal which is bonded to the metal pieces is confined between the spacers :and thereby prevented from brddging the metal articles. The wedge-shaping or tapering of the spacers :as illustrated assists in avoiding bridging by cutting through the contracting hard-surfacing material during the fusion operation.

The resulting hard-surfaced metal pieces which are thus formed can be readily disengaged from the spacers and machined to the desired dimensions without requiring further treatment.

FIGURE 3 is provided to illustrate the condition which results with the use of recessed spacers 11 instead of the extending spacers of the present invention. As can be seen, the hard-surfaced metal pieces 1 produced in this manner are rigidly connected by fused hard-surfacing material 9 and are not capable of being directly utilized or machined without considerable pre-treatment.

In the practice of the present invention it has been found that the present invention, while not limited thereto, is particularly effective for hard-surfacing articles, particularly steel articles, with the following hard-surfacing powders:

NICKEL ALLOY POWDER Percent Chromium 9 to 17 Silicon 3 to 4 Carbon 0.045 to 1.0 Iron 1.5 to 4 Boron 2.0 to 3.3

Nickel Balance COBALT ALLOY POWDER Chromium 21 Silicon 1.6

Carbon 0.1

Boron 2.4 Tungsten 4.5 Cobalt Balance COMPOSITE POWDER Nickel `alloy powder 50 Tungsten carbide powder 50 The following example is provided to illustrate the present invention.

Example I Several plain `carbon steel chain saw guide-bars s inch thick are arranged in a stack together with spacers in the manner il-lustrated in FIGURES 1 and 2 of the drawing. The spacers are about 46 inch thick and are formed of copper. The wedge-shaped portions of the spacers extend 1/16 inch above the stack.

A layer `of cobalt-base alloy powder about %4 inch thick is deposited on the stack by means of a spray-gun device in which the powder is pre-heated by an oxyacetylene flame. The composition of the powder is as follows:

Percent Chromium 21 Silicon 1.6

Carbon 0.1 Boron 2.4 Tungsten 4.5 Cobalt Balance The deposited layer is subsequently fused by means of an oxyacetylene torch at a temperature of about 2100 F. to 2200 F.

As a result of the fusion, the deposited metal contracts in volume and becomes strongly bonded to the guide-bar edges. All of the material which thus bonded to the edges is cut-through by the spacers and is entirely conned between the spacers.

From the foregoing description it can be seen that the present invention provides a simple and economical method for simultaneously hard-surfacing a plurality of metal yarticles whereby the necessity for further Itreatment prior to final machining is avoided.

What is claimed is:

l. In a process for providing an adherent hard-surface on metal edges by stacking together a plurality of metal pieces, depositing a hard-surface metallic powder in contact with selected edges of the metal pieces and heattreating the deposited hard-surfacing metallic material whereby the hard-surfacing metallic material is fused and bonded to the selected edges Iand reduced in volume, the improvement which comprises inserting spacers between adjacent metal pieces prior to the deposition of the hard-surfacing metallic powder thereon, said spacers being adhesion-resistant to the hard-surfacing material and extending beyond the selected edges of the metal pieces :and into the subsequently deposited hard surfacing metallic powder to the extent that, as a result of heat treatment of the deposited hard surfacing metallic material and the consequent reduction in volume thereof, said hard surfacing metallic material is cut through by the spacers.

2. A process in accordance with claim l wherein the extending portions of said spacers are tapered outwardly from the stacked metal pieces.

References Cited in the le of this patent UNITED STATES PATENTS 1,848,776 Godfrey Nov. 8, 1932 

1. IN A PROCESS FOR PROVIDING AN ADHERENT HARD-SURFACE ON METAL EDGES BY STACKING TOGETHER A PLURALITY OF METAL PIECES, DEPOSITING A HARD-SURFACE METALLIC POWDER IN CONTACT WITH SELECTED EDGES OF THE METAL PIECES AND HEATTREATING THE DEPOSITED AND HARD-SURFACING METALLIC MATERIAL WHEREBY THE HARD-SURFACING METALLIC MATERIAL IS USED AND BONDED TO THE SELECTED EDGES AND REDUCED IN VOLUME, THE IMPROVEMENT WHICH COMPRISES INSERTING SPACERS BETWEEN ADJACENT METAL PIECES PRIOR TO THE DEPOSITION OF THE HARD-SURFACING METALLIC POWDER THEREON, SAID SPACERS 